This invention relates generally to systems for tagging macro-organisms, and more particularly to an apparatus and method for tagging macro-organisms, such as fish, for subsequent detection and analyses.
For many years, biologists have been attempting to track the migratory patterns of animals. Particular emphasis has been placed upon studying the migratory habits of fish. There are several reasons for this, but perhaps the most important reason is because of the susceptibility of fish to environmental damage and to over-fishing. In recent years, the increasing need for hatcheries to propagate, grow and subsequently release migratory fish, such as salmon, steelhead and striped bass, has lead to a strong emphasis on developing an appropriate method for marking such fish. Because the fish are at the fingerling size when released from hatcheries, there has been a real problem with developing a system for indelibly marking such fish without affecting their swimming ability or their migratory habits.
A system has been developed in which a minute piece of stainless steel wire, commonly called a tag, is inserted into the cartilaginous region of the nose of the fish. The wire tag is typically magnetized so that when the fish return to spawn, biologists can electronically sort out those fish which have been tagged. The tags are indelibly marked so that the time and place of release can be determined. Two such systems are disclosed in U.S. Pat. Nos. 3,820,545 and 3,545,405 to Jefferts.
In a typical tag implantation operation, wire is intermittently advanced, cut and implanted into the cartilaginous region in the nose of the fish. Each fish is then passed through a large magnetic field, which tends to create the desired permanent magnetic charge in the implanted tag. Because the magnet must be large enough to receive the largest tagged fish, it is difficult to present a concentrated magnetic field to the wire tag. Also, because tag placement into the fish is not always coincidence with the linear extension of the fish, it is possible that the tag may not pass through the magnet in a linear disposition, which is the disposition which results in the strongest magnetic field being imparted to the tag. This is because some fish are not tagged in the nose, but rather are tagged in the gill area, where the disposition will be perpendicular to the linear extension of the fish.
It is imperative that a strong magnetic charge be imparted to the tag, because, as mentioned above, it may be as many as six years before the fish returns to spawn. Anything less than a strong magnetic charge might tend to dissipate, thus preventing electronic detection. Because of the inability to always impart a strong charge to the wire tags, extremely sensitive and therefore expensive tag detection equipment must be utilized to prevent any tagged fish from passing through the sensing mechanism without being detected.
Another drawback with conventional tagging systems is that they often result in the fish being impaled by an implantation needle, through which the tag is passed. This impaling process results in severe trauma to the fish, to an extent far greater than would be necessary by insertion of the tag alone. The injection can kill the fish or the injury can affect their migratory habits, which would defeat the purpose of the tagging operation.
It is therefore an object of the present invention to overcome the drawbacks and limitations of the prior art proposals. More specifically, the invention has as its objects:
(1) the provision of means for providing a much stronger magnetic field;
(2) to provide a method of applying a magnetic field to a fish tag in which the alignment of the tag passing through the magnetic process will be linear, rather than lateral, so that the ends of the tag will become the north and south poles, regardless of the ultimate positioning of the tag within the fish or other macro-organism;
(3) the provision of a system for applying a magnetic field to a fish tag which is simple, relatively inexpensive, which may be operated by one with little or no training, and which may be retrofitted into conventional tag implantation equipment;
(4) to provide a system which performs implantation and magnetization of a metallic fish tag in a single operation rather than the time-consuming and troublesome two-step process now being utilized;
(5) to develop a fish tag magnetization system which permits a reduction in the sophistication and therefore the cost of the detection equipment used for quality control and to recover and identify the tagged fish;
(6) the development of a tag magnetization system which is usable with tags having a wide variety of forms and materials; and
(7) to provide a tag implantation process which reduces the trauma to the fish being tagged.